In recent years, there is an increasing need for increased flexibility for electronics materials. In keeping with this, a great deal of research is being carried out on application of conjugate group polymer conductive materials, charge transfer materials as well as optical function materials. In particular, this has been put into practice as an electrolyte for solid electrolyte capacitor and as an antistatic agent for conductive function materials.
In order to lower the impedance in high frequency areas in the field of capacitors, aluminum, tantalum, niobium and other oxidized coatings (dielectric coating) are etched to provide a porous body coating and a layer (conductive polymer layer) made up of polyols, polythiophene and other π conjugate polymers is formed on this surface and a conductive polymer capacitor is used as a cathode.
It is of the utmost importance to further improve the conductance and the processing characteristics and to improve the environmental stability which involves heat resistance and moisture resistance of the conductive film obtained in order to expand the practicality of these π conjugate polymers. In particular, it is well known that conductive coatings cause desorption of dopants by heating over long periods of time and that the conductive declines.
A method for obtaining conductive coatings with improved heat resistance has been proposed which involves making a composite of an organic sulfonate compound as a dopant and heat stabilizer and a conductive polymer. For example, in Patent Document 1, a method is proposed which involves mixing an aromatic group sulfonate compound with a precursor monomer of polythiophene and polymerizing it and then forming a conductive coating. However, the method described in Patent Document 1 presents problems with the processing characteristics in that there is no suitable solvent for the conductive polymers obtained.
Another proposal has been made for producing a conductive coating by carrying out doping using sulfuric acid doping on polythiophene having a specific substituted group which has outstanding solubility in solvents and carrying out heat treatment such that the heat resistance is improved (for example, Patent Document 2).
The heat resistance of the conductive coating obtained has been improved by adding a basic compound to a composition containing water-soluble conductive polymers having a sulfonic acid group and/or a carboxy group (for example, Patent Document 3).